Field of the Invention
The present invention relates to a golf ball material, and more particularly to a golf ball material that can be suitably used as the material forming a part of the core and/or cover of a golf ball composed of a core of one or more layer and a cover of one or more layer.
Prior Art
Ionomer resins have hitherto been widely used as the cover material in golf balls. However, owing to the constant desire by users for golf balls endowed with a high rebound and a high durability, a variety of improvements are being carried out on such ionomer-based resins. In addition, innovations that entail mixing a low-cost resin such as polyethylene or ethylene-vinyl acetate copolymer (EVA) with an ionomer-based resin material have also been proposed in order to reduce costs.
One example is a golf ball that uses as the cover material an ionomer blend obtained by mixing a small amount of a medium- or low-density polyethylene with an ionomer-based resin (JP-A 60-145160). In addition, JP-A 60-80469, JP-A 1-32878, JP-A 4-126168 and JP-A 6-327794 describe, as golf ball materials, compositions which are obtained by blending an ethylene-vinyl acetate copolymer (EVA) with an ionomer-based resin. However, in all of these golf ball materials, the compatibility between the ionomer and these various types of polyolefins is poor, which has presented a problem in terms of the durability of the golf ball.
JP-A 11-276638 discloses that, by introducing a graft copolymer in which some or all of an ethylene copolymer has been graft-modified with an unsaturated dicarboxylic anhydride, the compatibility between the ionomer and the ethylene copolymer is improved, enhancing the durability of golf ball covers formed of such polymer compositions. However, a sufficient durability has not been achieved.
In addition, because the durability markedly declines when a low-cost resin such as polyethylene or ethylene-vinyl acetate copolymer (EVA) is mixed with an ionomer resin, art that improves the durability by adding and kneading an organic peroxide into this polymer alloy has been proposed. However, carrying out such a kneading operation takes time and effort. Moreover, in terms of the golf ball manufacturing operations, in cases where a compatibilizing agent is to be added to a polymer composition of an ionomer with a polyethylene, the polymer composition must first be subjected to a compounding step in an extruder, which takes a good deal of time and effort.
It is therefore an object of the invention to provide a golf ball composition composed primarily of an ionomer resin, which composition improves the ease and convenience of the golf ball manufacturing operations and enhances the durability of the resulting golf balls.